A hemodialysis treatment treats the blood of a patient by extracorporeally circulating the blood to purify it. In hemodialysis treatment, a dialyzer is used as a blood purification instrument for flowing therethrough a dialysate, and also connected to the dialyzer is a blood circuit for extracorporeally circulating blood of a patient through which the blood and the dialysate contact each other via dialysis membranes within the dialyzer so as to remove waste materials and excess water in blood (the removal of excess water is usually called as “ultrafiltration”). The blood purified by the dialyzer is returned into a body of the patient and, on the other hand, the blood waste material and excess water are discharged outside together with the dialysate via a dialysate discharging line.
The waste materials removed from blood contain urea, uric acid, creatinine etc. and it is found that a variation of the concentration of urea in blood is an effective indicator to show the dialysis efficiency. Accordingly, it has been proposed to monitor the variation in urea concentration to obtain proper dialysis efficiency. Although it is usually possible to know the variation in the urea concentration via a regularly performed blood examination, it is impossible to monitor the variation in urea concentration in real time during a dialysis treatment.
Accordingly, it has been proposed to arrange a discharged liquid concentration sensor on a dialysate discharging line so as to detect the variation in urea concentration (i.e. an indication such as “Kt/V”) in real time (see e.g. JP 2002-516722 below). Such a conventional discharged liquid concentration sensor usually comprises LED(s) (light emitting means) for irradiating light on to discharged liquid from a dialyzer, a light receiving element(s) (light receiving means) for receiving light from the LED(s) transmitted through the discharged liquid, and a detecting means for detecting a received light intensity received by the light receiving element(s) and is structured so that the concentration of discharged liquid can be detected based on the received light intensity detected by the detecting means.
However in the blood purification apparatus of the prior art, there is concern that conditions for measuring discharged liquid concentration would be varied by every dialysis treatments due to reasons of individual difference or deterioration due to the aging of light emitting means of discharged liquid concentration sensors, differences in composition of dialysate flowing through a blood purification instrument or degree of fouling of measuring parts and thus the accuracy in detection of the discharged liquid concentration would be decreased. These problems may similarly occur in other concentration detecting means for detecting concentration of liquids (liquids flowing during blood purification treatment and including blood etc. other than dialysate) comprising a light emitting means and light receiving means, and thus improvement in accuracy has been desired.
It is, therefore, an object of the present invention to provide a blood purification apparatus that can improve the detecting accuracy of liquid concentration and, thus, the reliability of the concentration detecting means.